Electronic brake systems for motor vehicles providing functions such as ABS, EBS, or similar functions are based on a mechatronics unit and comprise an electronic control unit (ECU) with an electronic controller that is connected to an electronic vehicle bus system. The mechatronics unit further comprises an accommodating member for hydraulic components (HCU), with electrohydraulic valves and a return pump. Besides, hydraulic conduits for wheel brakes and hydraulic connecting conduits for a master brake cylinder can be connected to the accommodating member.
In electronic brake systems of this type, a secondary fluid circuit is normally completely isolated from a primary hydraulic circuit, which connects the master brake cylinder to the wheel brakes in a conventional manner. This isolation causes difficulties in maintenance work or in the event of a new installation of a brake system because air bubbles in secondary fluid circuits cannot be removed easily by means of bleeding devices of the primary hydraulic circuits. Air inclusions, more specifically, unnecessary compressibilities, are principally not tolerable in a brake system.
Frequently a so-called end-of-line or vacuum filling is performed in vehicle production. More specifically, the hydraulic components of a vehicle brake system are mounted into the vehicle in a manner free from hydraulic fluid, hence in a dry fashion, in order to carry out a so-called vacuum filling with the provided hydraulic fluid at the end of the assembly line. In a first process step, the air disposed in the brake system is sucked off (vacuum phase), in a second step e.g. brake fluid under excess pressure is filled in (filling phase), and in a third step excessively filled-in fluid volume is sucked off (leveling phase). The filling and bleeding of the secondary fluid circuits, which are positioned mainly between normally closed electromagnetic valves (outlet valves) and pump suction valves, is a difficult task. It is necessary for this purpose to switch valves or the return pump of the brake system in a defined and synchronized manner in the individual bleeding and filling phases.
DE 38 06 840 C2 discloses a method of filling a hydraulic unit of an anti-lock control system. To remove air inclusions in the brake system, a bleeding computer equipped with a current supply unit, an operating unit, and a display unit are disclosed. The separate bleeding computer comprises a microprocessor having a special control program for the air removal. In order to actuate the anti-lock control system for air removal purposes, a plug of the cable harness in the vehicle is drawn off from the electronic controller of the anti-lock control system. The electronic controller is then connected separately to the bleeding computer. This allows executing bleeding sequences, in the course of which the return pump and electrohydraulic valves are actuated in order to remove air inclusions in secondary fluid circuits of the hydraulic unit using bleeding devices of primary fluid circuits (more specifically, by means of bleeder screws at wheel brakes).
EP 0 323 889 A1 discloses an anti-skid brake system having an anti-skid operating mode and a bleeding operating mode. In order to adopt the bleeding operating mode, the system, like in DE 38 06 840 C2, is connected to a diagnosis circuit by way of a diagnosis interface and a bleeding plug in order to obtain corresponding release data. In the absence of a correct connection at the diagnosis interface, a normal anti-skid operating cycle will commence. The brake system further comprises devices for disabling the bleeding operating mode when input signals of wheel speed sensors at the electronic control unit (ECU) indicate that the vehicle is moving.
The prior art methods for filling a vehicle brake system consequently found on that in each case there is provision of a separately connected process computer, in order to permit a bleeding or filling mode of an anti-lock control system. In the bleeding or filling mode, the process computer actuates the electronic controller of the anti-lock system and further predetermines a pressure time course for the control of the filling system. This requires in each case an electric connection between the process computer and the electronic controller of the brake system.
An object of the invention is to render possible an improved, more comfortable and also simplified execution of filling and bleeding processes. Another objective is to reach a higher rate of reliability when performing the mentioned processes.